Electronic circuit assemblies, such as direct current-direct current (DC-DC) converters and others, are often encapsulated and packaged as a single module for use in a variety of end applications. Encapsulation is desired to protect the circuit assembly from damage and degradation due to handling, soldering, and cleaning during manufacturing. Encapsulation also protects the circuit assembly from environmental conditions such as mechanical shock, vibration, exposure to moisture, and chemicals in end applications, which could be anything from consumer electronics to industrial systems or avionics. Encapsulation can also provide heat distribution and cooling for internal components by providing a thermal path to an external heat sink.
Some circuit assemblies may also require electromagnetic interference (EMI) shielding to reduce their electromagnetic emissions or susceptibility to external EMI.
Some conventional encapsulated circuit assemblies employ a pre-formed, non-integral conductive housing that surrounds the circuit assembly and is filled with an encapsulating (potting) compound. Some of these housings are in the form of a five-sided, “bathtub” configuration with an open side that leaves the encapsulant exposed. Others use a bathtub configuration in combination with a base plate to cover the open side. See U.S. Pat. No. 6,005,773 to Rozman. These types of encapsulated assemblies provide encapsulation, thermal path for heat dissipating components, and some EMI shielding. However, they suffer from increased size with respect to the main circuit board, limited EMI shielding, and susceptibility to liquid cleaning. The housing increases the size of the module, due both to the thickness of the walls and to the space required between the walls and the internal circuit board. The bathtub-configured housing provides EMI shielding only on five sides.
Other approaches encapsulate the circuit assembly and then cut the encapsulated assembly to size by sawing. Electrical leads are then connected to portions of the circuit assembly exposed during the sawing. See U.S. Patent Publication 2012/0287582 to Vinciarelli. This approach eliminates the housing, which has the potential for reducing the size of the module. However, the addition of external leads increases the overall dimensions of the module. In addition, this approach does not provide EMI shielding, and exposed edges of the circuit board remain susceptible to penetration by moisture or other contaminants.
Yet other approaches overlay circuit components mounted on a top side of a laminate substrate with an overmold body and an EMI shield coating. See U.S. Pat. No. 8,359,739 to Carey. However, these approaches do not permit use of circuit assemblies with electrical components on both sides of a printed circuit board.
Encapsulated electronic circuit assemblies that provide EMI shielding and address the drawbacks outlined above are needed.